Salinity and density share a positive relationship. As density increases, the amount of salts in the water—also known as salinity, increases. Various events can contribute to change in the density of seawater. Salinity can decrease from the melting of polar ice or increase from the freezing of polar ice.
In the brain especially in the eyes
If you are implying one these choices not needed for survival it would be parents only when you can survive on your own (I'm not that sure but I hope this helped the slightest but)
In chemical reactions involving enzymes, the substrate proteins are huge molecules that will only react with each other if they're aligned just the right way. If they are permitted to interact with the enzymes present, the won't collide and react often enough for the reaction to do any good.The enzymes align the molecules, basically acting like "molecule shepherds," showing them the way they need to react.This speeds up the reaction greatly, making things like digestion possible. Hope this is helpful